Insufficient information is available for selection of the most appropriate exercise levels for training and rehabilitation of coronary heart disease (CHD) patients with varying degrees of severity. Several studies indicate that vigorous exercise can be safely performed and that such training can elicit cardiovascular adaptations in selected CHD patients. We propose to compare the effects of low and high levels of regular supervised training over a two-year treatment period on cardiac adaptations among 200 patients with CHD documented by arteriogram or myocardial infarction. We will test the hypothesis that exercise of appropriate intensity and duration will safely effect cardiovascular adaptations. Recruitment, training and evaluation will take place at two affiliated clinical centers with long experience in cardiac rehabilitation. Eligible men will enter a pre-randomization program designed to identify and eliminate persons with adherence problems or poor motivation. Participants will be randomly assigned to high or low exercise groups and will be evaluated periodically with two independent exercise techniques - supine ergometer exercise and upright maximal exercise testing with gas exchange measurements. Both tests will include two-dimensional echocardiography pre- and post-exercise as well as during exercise with the ergometer. Comparison of the value of the two exercise techniques will yield important clinical information. The major outcome assessed will be the change in exercise ejection fraction at one year. Additional observations reflecting ventricular function, myocardial oxygen delivery capacity and metabolic alterations over time by treatment group will be noted. Results of this study will contribute to better understanding long-term cardiac adaptations with different physical activity levels and possibly the efficacy of secondary prevention. The implications for exercise prescriptions and patient evaluation in cardiac rehabilitation programs will be far reaching.